6 BULLETIN 866, U. S. DEPARTMENT OF AGRICULTURE. 
GENERAL CONSIDERATIONS. 
Butler (7) states that freshly prepared Pickering spray has a light- 
blue color, which becomes deep blue on standing. He found a 
neutral or acid Bordeaux, such as the Pickering sprays, to act more 
quickly than ordinary Bordeaux, and reported that the Pickering 
spray was less injurious to grapes than ordinary Bordeaux. He 
states that the toxic value of the unit copper is the same in acid, 
neutral, and alkaline Bordeaux, but is more available for immediate 
action in the Pickering than in the ordinary Bordeaux sprays. 
According to McAlpine (15), who compared the results of Pickering 
with those of standard Bordeaux sprays on apple trees, the two 
varieties are equally effective in controlling black spot (Fusidadium 
dendriticum) . The limewater Bordeaux adhered just as well as the 
standard Bordeaux, and had the additional advantages of being free 
from gritty particles, of acting at once on the spores of the fungus, 
and of containing a much smaller percentage of bluestone. The 
check trees gave 92.5 per cent of good fruit, indicating that the 
black spot was not sufficiently severe to give definite results. 
F. de Castella (9) states that Pickering's claims concerning the 
greater efficacy of the limewater sprays are not borne out in practice. 
He reports that after extensive trial they have been foxmd decid- 
edly inferior to 2 per cent Bordeaux and that the use of Pickering 
sprays can not be recommended. He considers the Woburn or 
Pickering paste sold in England to be satisfactory but not superior 
to Bordeaux. The greater solubility of the tetra-cupric sulphate 
seems to be a defect rather than an advantage according to this 
writer, for the reason that, while more active at first, it is removed by 
heavy rains more readily than the ordinary Bordeaux deposit, thus 
rendering the duration of the protection insufficient. No data are 
given by this writer to substantiate his claims. 
PURPOSE OF PRESENT INVESTIGATION. 
If the results obtained by Pickering in the laboratory in England 
hold true under field conditions in America, it is obvious that a great 
saving in copper in this country may be effected. This investigation 
was planned, therefore, for the purpose of outlining a practical 
method of preparing a copper fungicide which would be more effective 
per unit of copper than standard Bordeaux. The experiments were 
conducted with the following primary objects in view: 
(1) To determine whether sprays made in accordance with the 
various Pickering formulas (p. 3) were effective when applied under 
American field conditions. 
(2) To ascertain how much copper in the form of the different 
Pickering formulas is required per given quantity of spray to insure 
effective control of fungous diseases. 
